High frequency transformer



Oct. 27, 1931; .1. H. PRESSLEY HIGH FREQUENCY TRANSFORMER I Filed Aug. 3, 1929 2 Sheets-Sheet l Oct. 27, 1931. J. H. PRESSLEY HIGH FREQUENCY TRANSFORMER Filed Aug. 3, 1929 2 Sheets-Sheet 2 INVENTOR v Press/6y I BY M, 9 W M ATTORNEYS Patented Oct. 27, 1931 UNITED STATES PATENT OFFICE JACKSON H. PRESSLEY, OF MARION, INDIANA, ASSIGNOR TO CORPOBA- TION, OF JERSEY CITY, NEW JERSEY, A CORPORATION OF DELAWARE HIGH FREQUENCY TRANSFORMER Application filed August 3, 1929. Serial No. 888,214. f

This invention relates to high-frequency transformers, and more particularly to transformers of this type which are utilized as an essential part of couplin networks adapted to provide substantialFy uniform amplification over a desired frequency range when interconnecting the successive tubes of a high-frequency thermionic amplifier.

An object of the invention is to provide structural features of high-frequency transformers which accomplish the above results with high efliciency.

A second object of the invention is to provide transformers of the above type which, in addition to their function of providing substantially uniform amplification over a frequency range, are also adapted, when utihzed in conjunction with a suitable capacity element, for neutralizing the effect of the grid-to-plate interelectrode capacity electrostatically coupling the grid and plate circuits of a thermionic amplifier.

The subject of uniform gain coupling networks of the type mentioned above is described fully in application for United States Letters Patent Serial No, 120,045, filed July 2, 1926, and United States Letters Patent 1,763,380, issued June 10, 1930, both in the name of C. E. Trube, which descriptions are made a part of the present specification. Since the present invention is limited to transformers suitable for use in coupling networks, the circuits adapted to accomplish substantially uniform gain in thermionic amplifier circuits will be referred to herein only so far as is necessary to point out the features of the present invention.

Referring to the drawings, Fig. 1 shows in circuit diagram form two thermionic amplifier tubes interconnected by a uniform gain coupling network employing one of the novel transformers of the present invention. The circuit of Fig. 1 is identical with that disclosed in Fig. 6 of the drawings accompanying the Trube patent referred to above,

. except for the addition of the neutralizing capacity C For convenience in comparing the two drawings the circuit elements have been similarly designated,

Figs. 2' and 3 disclose the structural dematically in Fig. 4. Fig. 6 shows an end elevation of the transformer as viewed from the left of Fig. 5; while Fig. 5 shows a cross section thereof taken along the line w-m of Fig. 6. X

Referring now to Fig. 1, a pair of thermionic tubes 10 and 11, each having grid G, plate P and filament F electrodes, are connected in cascade by means of a uniform gaincoupling network comprising transformer T and ca? pacities C and C Batteries 12 provide the necessary direct current to the plate circuits of the tubes, while batteries 13 provide negative grid biasing potential. The transformer T comprises a secondary winding L and a pair of primary windings L and L Thesecondary winding shunted by a variable tuning capacity O is connected between grid and filament of tube 11. The primary winding L shunted by the fixed capacity C is con nected series opposing with the primary winding L between the plate and filament of tube 10. The winding L contains relativelymany turns and hence a high inductance compared to L the winding L has only a few turns compared to L and hence a.

capacity C so that this parallel circuit has an impedance which decreases with increase in frequency over the tunin range, whereas, L has an impedance whic increases with frequency. The windings L and L are connected in opposite directions, but produce additive effects in the winding L due to the fact that over the operating frequency range hence produce additive magnetic fields. By suitably proportioning the various elements of the coupling network, the unlform gain coupling is obtained as described in the Trube application and patent referred to above.

In order to neutralize the interelectrode coupling capacity C occurring between the plate and grid of tube 11, a neutralizlng capacity G is connected from the plate P of tube 11 to a point between the primary windings L and L With the circuit arrangement shown and with winding L properly poled with respect to winding L neutralization is attained when the following relation holds true.

where M is the mutual inductance between the windings L and L Under the conditions of Equation (1) stated, a current flowing from the plate to grid thru thecoupling capacity C due to a disturbance initiated in the plate circuit will set up a magnetic flux in secondary winding L which is equal and opposite to the flux produced therein as a result of the current simultaneously flowing thru neutralizing capacity C, and neutralizing winding L, with the result that no voltage will be induced between the id and filament of tube 11 due to such a disturbance in the plate circuit.

In order to have the neutralization of the plate-to-grid capacity C effective over the entire tuning frequency range of the capaclty C it is necessary to have as close a magnetic coupling as possible between windings L and L Furthermore, in order that the neutralization thus obtained be not disturbed by the primary circuit associated with tube 10, it is required that the coupling between windings 1 and L be as loose as possible consistent with the necessary degree of coupling between windings L and L It has been found that the uniform gain coupling network operates most satisfactorily when the coupling between windings L and L is not too loose and not too close, i. e., when the coupling is about 15% to 20%, which might be termed a moderate degree of coupling. Since a coupling of about is, in practice, obtainable between windings L and L it is possible to have the degree of coupling between windings L and L amount to only a few percent by suitably positioning windings L and L relative to L in the manner explained below. This latter is a very L desirable condition since, as was explained above, it prevents disturbances of the neutralization due to currents in the primary circuit.

From what has been stated above, it will be seen that the transformer T must be designed to meet a number of conditions which may be summarized as follows. The inductance L must be large, and the inductance L small relative to L The coupling between L and L must be of the order of 20%, and that between L and L as close as possible, say around 70%, while that between L and L, must be loose and of the order of only a few percent. These ideal coupling conditions are mutually at variance so that special placing of the coil windings is required for obtaining the best compromise result.

Referring now to Figs. 2 and 3, a coil is shown which meets the above conditions in a highly eificient manner. Referring more particularly to Fig. 3, the transformer comprises a spool 20 of insulating material preferably of wood, such as maple, which spool has a sharply constricted portion 21 adja cent one end for reception of the primary winding L which comprises an annular winding'of a plurality of layers. At its 0pposite end, the spool 20 has formed thereon a pair of shoulders 21 and 22 of different diameters arranged in step-like relation. A tubular section 0 of insulating material, such as bakelite, or the like, is adapted to have one end snugly fitted around the shoulder 22 of smaller diameter formed on the spool 20, and is of such length as to extend considerably beyond the constricted end of the spool 20, as shown. The secondary winding L comprises a single layer of wire uniformly wound about the tubular section 0 commencing at a point adjacent the shoulder 22 and extend ing somewhat beyond the winding L The arrangement shown, wherein the winding L has a diameter considerably less than that of the winding L and is positioned coaxially therewithin, permits a moderate degree of magnetic coupling, say of the order of 15% to 20%, to 'be obtained between the windings L and L T A second tubular section M of insulating material, preferably stiff paper, has one end fitted snugly about the shoulder 21 of spool 20, the tubular section being of. such length as to extend beyond the constricted end of the spool 20, but not so far as the tubular sectionO. This arrangement, wherein the secton 0 projects beyond the section M, permits section 0 to be easily grasped and removed in order to repair vany defects in the winding L The small primary winding L is wound about the tubular section M and comprises a single layer of wire uniformly wound substantially between the limits of the winding Windings L and L as will be seen from the dimensions given below, are of only slightly differing diameters so that with the coaxial positioning of the windings as shown, wherein winding L is positioned within winding L a high degree of magnetic coupling isobtained between the two. Furthermore, by positioning windings L and L, on

Fig. 3 by the small letters.

21 inch b=% inch 0 1% inches d li inches e inch f inch inch i=% inch j inch k 1 1% inches 1 1 2 inches m 2 inches n 34; inch M .025. inch paper 0 inch bakelite The data on the windings is as follows:

Winding L comprises 14% turns of #36 B. & S. gauge D. S. .6. wire uniformly wound over a length of 1% inches. A

Winding L comprises 135 turns 'of #28 a B. 86 S. gauge enameled wire uniformly wound over a length of 1 1 inches.

Winding L comprises 220 turns of #36 B. & S. gauge D. S. C. wire having a length of inch uniformly wound in a suflicient number of layers to provide the specified number of turns. j

The following electrical measurements were obtained at 1,000 cycles for atransformer having the specifications given above. The self-inductances of the windings expressed in microhenrys were as follows:

Winding 1 1.3 microhenrys I Winding L =252 microhenrys Winding L =500 microhenrys the mutual inductances were;

M =23 microhenrys M =67 .3 microhenrys I where M designates the mutual inductance,

250 mmf. The resonant frequency of the primary circuit L G with such inductance and capacity values is 450 kc., and the maximum required capacity range of the tuning condenser C is from 40 to 350 mmf. adapted to tune the coupling network over a range of from about 550 to 1500 kc. A neutralizing capacity C of about 85 mmf. was required for a UX226 type vacuum tube having a grid-plate capacity C of about 7 mmf. The transformer is designed for use in a copper or aluminum shielding can of a diameter of 2% inches and length of 3 inches,and the above electrical constants for the transformer are given with the same mounted in such a can.

Fig. 4 shows a circuit arrangement utilizing a slightly modified type of transformer from that shown diagrammatically in Fig. 1. In Fig. 4, in order to utilize a neutralizing capacity C of approximately 60 mmf.

in conjunction with the same type of tube, it is required that the neutralizing winding have a larger inductance than that of the small primary winding L To accomplish this a winding L comprising a few turns is interposed between the neutralizing casacity C and the connection to winding L ther wise the circuit arrangement of Fig. 4 is similarto that of Fig. 1.

Fig. 5 discloses the structural details of the transformer T shown diagrammatically in Fig. 4. Referring to Fig. v5, the large primary winding L comprising an annular coil of several layers is wound in a circumferential groove 30 formed in a s 001 31 of suitable insulating material, pre erably impregnated wood. A suitable tubular section D of insulating material, preferably bakelite, has one end fitted snugly around the spool 31 as shown. The secondary windin L comprising a single layer is uniform y wound about the tubular section D from a point adjacent the winding 30 to a oint some distance therefrom. A thin strip of insulating material 1, preferably celluloid, is wrappe snugly about the winding L; adjacent the end thereof distant from winding L and a neutralizin winding N comprising a single layer of re atively few turns is wound snugly about the celluloid strip 1. Thiswinding N terminates in terminals 3 and 5 and has an additional terminal 4 tapped at an intermediate oint for forming the winding L and ounting lugs 9 and 10 are suitably affixed to the tubular section D.

By positioning the winding L coaxially with winding L and adjacent one end thereof, a moderate degree of magnetic coupling is obtained between the windings. A close degree of magnetic coupling is obtained between winding L and windings L and L, due to the close physical proximity of the two. The required small degree of magnetic coupling between windings L, and N and A inch B 1 4 inches D inch bakelite E =2 inches H inch I =.01 inch celluloid J inch K inch M 5% inch P inch The electrical constants of the transformer when placed in a cylindrical copper can having a 2% inch diameter and a length of 3 inches and measured at 1,000 cycles, were as follows: For self-induotances of the windings expressed in microhenrys;

L 6.9 microhenrys L L 36.4 microhenrys L 245 microhenrys L 1710 microhenrys The mutual inductances were:

M 16.3 microhenrys M 42.5 microhenrys M 92.5 microhenrys The coupling coeificient between the small primary L and the secondary L was 40.2 percent, between the neutralizlng winding N and L is 63 percent, and between the large primary L and the secondary L was 15 percent.

The winding data is as follows:

The large primary winding L consists of 270 turns of #36 B. & S. gauge D. S. 0. wire.

The secondary winding L comprises 131 turns of #28 B. & S. gauge enameled wire.

Winding L comprises 18 turns and L comprises 9% turns of #36 B. & S. gauge D S. C. wire.

In either of the foregoing coil designs, L, can have the alternative construction of the so-called universal type of multi-layer coils.

I claim:

1. A high-frequency transformer comprising a secondary distributed cylindrical winding, a first primary distributed cylindrical winding of few turns relative to and closely wound about the secondary for providing a high degree of magnetic coupling therewith, and a second primary annular winding of compact structure of many turns relative to and ositioned within said secondary and of sufficiently smaller diameter than said secondary to provide a moderate degree of magnetic coupling therewith, the aforesaid couplings between said primary and secondary windings being obtainable consistent with a relatively low degree of magnetic coupling between said primary windings resultant upon the positioning thereof on opposite sides of said secondary winding.

2. A high-frequency transformer comprising in combination a spool of insulating material having a sharply constricted portion adjacent one end thereof for reception of a compact annular winding positioned therein, said spool having formed at the opposite end thereof from said constricted portion a pair of shoulders of different diameters in stepped relationship, a tubular section of insulating material fitted about said shoulder of smaller diameter and extending beyond the opposite end of said spool, a distributed winding wound uniformly about said tubular section from a point adjacent said last mentioned shoulder to a point beyond said annular winding, a second tubular section of insulating material fitted about said shoulder of larger diameter and extending beyond the opposite end of said spool, and a distributed winding wound uniformly about said second tubular section substantially within the limits of the distributed winding first mentioned.

3. A high-frequency transformer comprising in combination a tubular section of insulating material, a first distributed winding comprising a single layer wound uniformly about said section between certain limits thereof, a second tubular section of insulating material of larger diameter than the first and surrounding the same, a second distributed winding of few turns relative to said first winding wound uniformly about said second tubular section substantially within the limits of said first distributed winding, a spool of insulating material of smaller diameter than said tubular section first mentioned and positioned within the same, said spool having a sharply constricted portion for reception of a compact annular winding wound thereabout of many turns relative to said first winding, and means for maintaining said windings positiloned as aforesaid in fixed spacial relations 1p.

4. A high-fre uency transformer adapted for use in a uni orm gain couplin network associated with the input to a t ermionic tube having grid filament and plate electrodes, comprising in combination, a distributed cylindrical secondary winding, a first distributed cylindrical primary winding of few turns relative to and closely wound about said secondary for providing a high degree of magnetic cou ling therewith, and a second compact annu ar primary winding of many turns relative to and positioned within said secondary and of suifioiently said secondar smaller diameter than said secondary to provide a moderate degree of magnetic coupling therewith, the aforesaid couplindgfi1 between said primary and secondary win gs being obtainable consistent with a relatively low degree of magnetic coupling between said (primary windings as compared with the egree of coupling between each primary winding and the secondary winding, resultant on the positioning thereof upon opposite sides of said secondary winding.

5. A high-frequency transformer comprising first and second primary windings and a secondary winding, said first primary w1nding bein positioned within said secondary and sai second primary winding being wound over said secondary winding, the distance between said first primary winding and said secondary winding being considerably greater than the distance between said second primary winding and said secondary wmding, whereby the coefiicient of coupling beatween said second primary winding and said secondary winding is considerably greater than the coeificient of coupling between said first primary winding and said secondary winding, and wherebythe coefiicient of coupling betweensaid first and second primar win ings is substantially less than the coe ficient of couplin between said first primary winding and sai secondary winding.

6. A high-frequency transformer comprising first and second primary windings and a secondary winding, said first primary winding being positioned within said secondary,

'andsaid second primary winding being wound over'said secondary winding, the distance between said first primary winding and winding being considerably greater than t e distance between said second rimary winding and said secondary winding, whereby the coefiicient of coupling between said first primary winding and said secondary winding is considerably greater than the coefficient of couplin between said first and second primary win ings, and the coefiicient of coupling between said first and t1al to said neutralizing condenser to neutralsecond primary wind ngs is substantially less than the coeflicient of coupling between said second primary winding and said secondary windin 7. A high-frequency transformer according to claim 6 in which the coeflicient of coupling between said second prima winding and said secondary winding is a ut per cent, and the coefiicient of coupling between said secondary winding and said first primary windin is about 20 per cent, and the coefiicient 0 coupling between said first and second primary windings is less than 8 r cent. I

8. A high-frequency transformer'comprisin first and secondrimary windings and a he ical secondary winding, the first of said primary windings being located within said secondary winding, the second of said primary windings being located outside said secondary winding, said first primary winding being a compactly wound 'multi-layer winding having a higher inductance than said secondary winding and placed a substantial distance inside said secondary winding, and said second primary winding being of lower inductance than said secondary winding and being helically wound over and very close to said secondar winding, whereby the coefiicient of coup ing between said second primary and said secondary windings is much higher than the coefiicient of coupling between said first primary and said secondary windings, and the coefiicient of coupling between said first and second primary windings is much lower than that between said first primary and said secondary windings.

9. A high-frequency transformer adapted to couple a source of high-frequency signals to the input of a space discharge device which comprises a cathode, anode and control electrode, said device having undesirable capacity between said anode and said control electrode and being provided with a condenser connected to said anode for neutralizing said undesirable capacity, said transformer comprising first and second primary windings for conneclion in series with said source, a secondary winding for connection to said cathode and control electrode, said secondary winding being helically wound, said first primary winding being compactly wound and located at a substantial distance within said secondary winding, said second primary winding being helically wound directly over, and close to, said secondary winding, whereby the degree of coupling between said second primary windin and said secondary winding is close and the coupling between said first and second primary windings is very loose, relative to the coupling between said secondary winding and said first primary winding and whereby said second primary winding is adapted to provide proper potenize said undesired capacity.

10. A high-frequency transformer adapted to couple a source of hi h-frequency signals to the input of a space ischar e device containin an anode, cathode an grid and to provi e the proper potential to effect grid circuit neutralization of the anode-grid capacity of said device, said transformer comprising first and second primary windings for connection in series with said source, a secondary windin cathode and said grld, said secondary winding being wound in a sin le layer on a cylindrical form, said secon primary windin being wound in a single layer on a second cylindrical form surrounding said secondary winding, and said second primary winding for connection to said having fewer turns than, and being located close to, said secondary winding whereby the degree of coupling between said second primary winding and said secondary winding is close, said first primary winding being compactly wound in a spool situated at a substantial distance Within said secondary winding and having a greater number of turns than said secondary winding, whereby the coupling between said first primary winding and said secondary winding is moderate and whereby the proper potential is developed across said second primary winding to efiect said neutralization.

In testimony whereof I aiiix my signature.

JACKSON H. PRESSLEY. 

